We have screened mutants of the mouse for visual defects by measuring the optokinetic nystagmus (OKN). Mice bearing the gene reginal degeneration (rd) were excluded from the screening. The results of this screening test are as follows. "Neurological" mutants such as reeler, weaver, and Purkinje cell degeneration all had normal OKN. However, some mutants that lacked pigmentation in some parts of their bodies lacked OKN. By studying the pigmentation in the eye of each of these mutants we have made the correlation that mutants that lack pigmentation in the pigment epithelium also lack OKN. However, pigmentation mutants that have normal pigmentation in their pigment epithelium seem to have normal OKN. We have measured retinal ganglion cell projections to the lateral geniculate nuclei and pretectal nuclei and have found these to be abnormal for each of the mutants that lacks pigment epithelial pigmentation. The proposed work will extend the above work by determining exactly which nuclei receive incorrect projections and by investigating more mutants that have abnormal pigmentation in their pigment epithelia and allelic mutations that have normal pigmentation in their pigment epithelia. One of the mutants with reduced pigment epithelial pigmentations is pearl. This mutant has reduced sensitivity (measured using retinal ganglion cell responses, in the dark-adapted condition, in intact, anesthetized mice). A preliminary finding is that the reduced sensitivity does not occur for these mutants when retinal ganglion responses are studied in the isolated, superfused retina. The further goal of the proposed work will be to determine the cause for the restoration of normal sensitivity in the isolated retina.